Low impedance memory bitline eliminating precharge
View Patent ↗A memory system using low impedance memory bitlines that eliminate the need for a precharge clock signal. An equilibration circuit controlled by a reference voltage is connected to the first and second bitlines of a memory cell and is operable to maintain a predetermined equilibrium condition between the first and second bit lines. The equilibration circuit is operable to generate an impedance load in the first and second bit lines at a level that allows generation of differential signals in the bit lines. The memory cell bitlines can move from a sensed state “low” to the opposite state “high” without an intervening precharge, thereby providing a significant increase in performance.
1. A memory system, comprising:
a memory cell;
first and second bitlines operably connected to said memory cell;
a write line operably connected to said memory cell; and
an equilibration circuit controlled by a reference voltage, said equilibrium circuit connected to said first and second bitlines, said equilibrium circuit comprising first and second pMOS devices in series with said first and second bitlines, respectively, and a third pMOS device connected between said first and second bitlines and wherein the gates of said first, second and third pMOS devices are connected to said reference voltage, wherein said first, second and third pMOS devices operate as resistors in the linear region of MOSFET device operation, and wherein said equilibration circuit is operable:
to maintain a predetermined equilibrium condition between said first and second bit lines; and
to generate an impedance load in said first and second bit lines at a level that allows generation of differential signals in said bit lines.
2. The memory system according to claim 1 , wherein the resistance of said first, second and third pMOS devices is determined by the gate-source voltage of said pMOS devices.
3. The memory system according to claim 2 , wherein said write line is operably connected to said memory cell by at least one transfer gate.
4. The memory system according to claim 3 , wherein said transfer gate comprises an nMOS device and wherein said reference voltage is related to the gate drive current of said transfer gate.
5. The memory system according to claim 4 , wherein said reference voltage is controlled by a reference circuit that is operable to change said reference voltage to compensate for variations in operating characteristics of said first, second and third pMOS devices.
6. The memory system according to claim 5 , wherein said reference circuit is further operable to change the reference voltage to compensate for variations in the operating characteristics of said nMOS device comprising said transfer gate.
7. The memory system according to claim 6 , wherein said reference circuit comprises a current mirror.
8. A method for controlling operation of a memory system, comprising:
storing information in a memory cell;
generating a predetermined equilibrium condition between first and second bitlines operably connected to said memory cell using an equilibration circuit connected to said first and second bitlines, said equilibrium circuit being controlled by a reference voltage and comprising first and second pMOS devices in series with said first and second bitlines, respectively, and a third pMOS device connected between said first and second bitlines, wherein the gates of said first, second and third pMOS devices are connected to said reference voltage and, wherein said first, second and third pMOS devices operate as resistors in the linear region of MOSFET device operation; and
controlling the content of information in said memory cell with a write line operably connected to said memory cell.
9. The method according to claim 8 , wherein the resistance of said first, second and third pMOS devices is determined by the gate-source voltage of said pMOS devices.
10. The method according to claim 9 , wherein said write line is operably connected to said memory cell by at least one transfer gate.
11. The method according to claim 10 , wherein said transfer gate comprises an nMOS device and wherein said reference voltage is related to the gate drive current of said transfer gate.
12. The method according to claim 11 , wherein said reference voltage is controlled by a reference circuit that is operable to change said reference voltage to compensate for variations in operating characteristics of said first, second and third pMOS devices.
13. The method according to claim 12 , wherein said reference circuit is further operable to change the reference voltage to compensate for variations in the operating characteristics of said nMOS device comprising said transfer gate.
14. The method according to claim 13 , wherein said reference circuit comprises a current mirror.
15. A digital processing system, comprising:
a datapath module;
a control module;
an input-output module; and
a memory cell;
first and second bitlines operably connected to said memory cell;
a write line operably connected to said memory cell; and
an equilibration circuit controlled by a reference voltage, said equilibrium circuit connected to said first and second bitlines, said equilibrium circuit comprising first and second pMOS devices in series with said first and second bitlines, respectively, and a third pMOS device connected between said first and second bitlines and wherein the gates of said first, second and third pMOS devices are connected to said reference voltage, wherein said first, second and third pMOS devices operate as resistors in the linear region of MOSFET device operation, wherein said equilibration circuit is operable:
to maintain a predetermined equilibrium condition between said first and second bit lines; and
to generate an impedance load in said first and second bit lines at a level that allows generation of differential signals in said bit lines.
16. The digital processing system according to claim 15 , wherein the resistance of said first, second and third pMOS devices is determined by the gate-source voltage of said pMOS devices.
17. The digital processing system according to claim 16 , wherein said write line is operably connected to said memory cell by at least one transfer gate.
18. The digital processing system according to claim 17 , wherein said transfer gate comprises an nMOS device and wherein said reference voltage is related to the gate drive current of said transfer gate.
19. The digital processing system according to claim 18 , wherein said reference voltage is controlled by a reference circuit that is operable to change said reference voltage to compensate for variations in operating characteristics of said first, second and third pMOS devices.
20. The digital processing system according to claim 19 , wherein said reference circuit is further operable to change the reference voltage to compensate for variations in the operating characteristics of said nMOS device comprising said transfer gate.
21. The digital processing system according to claim 20 , wherein said reference circuit comprises a current mirror.